That sounds great. I did something similar for the medium grey open fresco.
I'd also consider contrasting buttons. White MOP or blonde horn might be too much, but maybe tan horn? I did an unstructured dark navy fresco suit from the last EFF with blonde horn buttons, though I did flap pockets that time.
Southwick's smoke MOP buttons look amazing with anything navy. Though, as @cyclohexane suggests, the tan horn (U6) buttons are the unsung heroes of Southwick MTOs. They add a pop of color without being too loud.